The present invention relates generally to systems and methods for broadcasting information, and more particularly to systems and methods for broadcasting information, data or content, to intermittently available receivers, such as mobile receivers.
A conventional approach to broadcasting data to a large number of receivers is referred to as the “data carousel” protocol. Using this approach, broadcast data is usually split into equal-sized packets, each of which forms a section in a data carousel. Each section is then broadcast over a specific period of time, and the data carousel continues to repeat to transmit those data portions that one or more receivers did not receive. Usually the broadcasting terminal (e.g., a network server, satellite or terrestrial transmitter) will need to transmit the data in the repeated fashion many times since it is usually not possible to synchronize the receivers to receive the transmitted data during one transmission period. The continued transmission of the same data set reduces the transmitter's efficiency, and as the transmission cycles continue, successively fewer receivers benefit from the transmission.
Further complicating this approach is the observation that in many applications, each receiver, through its normal course of operation, may itself be switched on and off during a transmission period. Systems such as automotive-based data receivers (e.g., on-board navigation systems), global positioning systems, cellular handsets, and portable computers employing 802.11x wireless communication protocols are but a few examples of such receivers. The sheer number of these receivers combined with their intermittent operation greatly increases the number of transmission cycles required to ensure that a large majority of the receivers have received all data segments.
Forward error/erasure correction (FEC) represents a conventional improvement to the data carousel approach. In this approach, a forward error correction algorithm is applied to each of the data segments, producing redundant data for that segment. This approach is an improvement over the data carousel, as the receiver needs only receive a subset of each data segment to correctly decode it. This results in fewer transmission cycles being needed to disseminate the broadcast data to a large majority of receivers. While providing an improvement, the FEC data carousel systems still has the disadvantages that: (1) each receiver must still receive a relatively large portion of each data segment; and (2) prior art FEC codes used in such data carousel systems, such as Reed-Solomon codes, require computational resources well beyond that which is available or commercially feasible in many applications. As noted above, many of the intermittently available receivers will not remain continuously on during a transmission period, and accordingly, a large number of repeated transmission cycles will be needed. It is expected that in practice some receivers will receive all segments quickly, while others will take a long time, resulting in the aforementioned condition of repeatedly broadcasting previous data over a long period to achieve a high rate of successful receptions.
What is therefore needed are systems and methods for broadcasting data to receivers, including mobile and intermittently available receivers, in a more efficient manner.